U.S. companies have sold more than $245 billion — or almost a quarter of all bonds issued this year — in only seven weeks. And investors can't get enough, driving down borrowing costs for even the junk-rated issuers to 14-month lows.

“To borrow a phrase from a couple great singers in history, it's feeling a little bubblelicious in the credit markets,” Mike Swell, co-head of global portfolio management for fixed income at Goldman Sachs Asset Management, said in an interview on Bloomberg TV.

With the month not even half over, more than $30 billion in issuance this week has already cemented August as the busiest since 2010 for debt sales by blue-chip companies, according to data compiled by Bloomberg. The high-yield market is also showing signs of life, with junk-rated companies selling more than $11 billion of notes this month, compared with $14.5 billion in July.